The present invention relates to a mechanical acceleration device as used in machines for welding hollow items of cylindrical or similar shape. In conventional welding machines of the type in question, discrete strips of metal emerging from a transfer station are rolled into a cylindrical shell with the two edges for welding offered one to the other. The feed direction of the strips runs perpendicular to the transfer station runout, and accordingly, a system must be provided that will engage the strip, already invested with cylindrical shape around a guide rail but as yet motionless in the direction of its longitudinal axis, and carry it toward the station where the overlapping edges are ultimately welded together, at which point its velocity will be dictated by the operating speed of the welding components.
In short, the hollow cylindrical elements must be accelerated along the longitudinal feed direction they are required to follow.
To this end, conventional type welding machines currently utilize a conveyor consisting in a pair of chain loops occupying vertical planes, which are set apart at a distance such as allows passage of the cylindrical element and afford a plurality of pins or teeth positioned in matching pairs, which engage the rear circumferential edge of each shell and push it toward the successive work stations. In order to protect the can shells from too sharp an acceleration, and ultimately from any impact likely to cause a permanent deformation of the circumferential edge that would give a substandard end product in terms of quality, such chains are invested with non-harmonic movement at a variable velocity of V.sub.o .+-.d.sub.V, starting at the lower velocity of Vo-dV and carried forward, accelerating to a velocity Vo+dV commensurate with the rate of production required at the welding station.
Such an effect is achieved using a cam type linkage of particularly complex mechanical design, as disclosed in application no. 3400 A/89 for Italian patent filed by the same applicant.
The system in question betrays a further limitation however, given its inability to reach still higher operating speeds as increasingly demanded by the users of such welding machines, without occasioning damage to the can shells as a result of impact on the circumferential edges, which inevitably occurs during the pushing action of the chain teeth unless the machine is faultlessly adjusted.
Accordingly, the object of the present invention is to overcome the drawbacks mentioned above.